Current regulating ballast tube



Sept. 15, 1959 c. c. MINTER CURRENT REGULATING BALLAST TUBE Filed Jan. 28, 1957 vrrv 5/ I p H 5 fvl lvl r INVENTOR CLARKE C. MINTER ATTORNEYS United States Patent 2,904,764 1, CURRENT REGULATING BALLAST TUBE Clarke C. Minter, Washington, D.C. Application January 28, 1957 Serial No. 636,843

6 Claims. (Cl. 338-20) (Granted under Title 35, U5. Code (1952), see. 266) change in voltage. The tubes of the prior art usually consist of a small iron wire filament mounted in a sealed glass tube containing hydrogen at a suitable low pressure. Ballasting action is not limited to the above combination, since other tubes have been made by a combination of other metal filaments and other gases, however, the ironhydrogen combination is the most used and best results have been obtained from this combination.

In order to have ballasting action the metallic filament must have a high temperature coefiicient of resistance that increases with temperature such that the resistance of the filament increases more rapidly than the temperature as it is heated. When there is an increase in voltage across the filament, the wire filament of the tube is heated thereby raising the resistance thereof to electrically account for the increase in voltage, that is, the increase in voltage is converted by the filament of the ballast tube into resistance rather than being divided across the other portions of the circuit, thereby maintaining the current constant.

In order for ballasting to occur, temperature and resistance differences must exist in the portion of the current heated filament to cause hot-spots, these differences are brought about by (1) local differences in the diameter of the wire and (2) cooling effect of the supports holding the filament. In the straight filament type ballast tube in which local differences occur, diameter differences of the filament cause ballasting by creation of hot-spots at the nonuniform points. The ballasting action of different tubes vary since the wire filaments are not uniformly made and the ballasting action is only for a short range of voltage difference. Due to the cooling of the filament by the supports there is substantial time lag before the current becomes steady after a change in voltage.

In the prior art ballast tubes, not only is there a time lag in current stabilization after a change in voltage but a ice Yet another object is to provide a ballast tube which will provide ballasting action over a wide range of voltage change.

Still another object is to provide a ballasting tube having nonuniform heating in an isolated filament of uniform diameter.

Other and more specific objects of this invention Will become apparent upon a more careful consideration of the following detailed description when taken together with the drawings, in which;

Fig. 1 is a cross-sectional view of a ballast tube according to this invention having a filament of uniform diameter in the form of a helix having a graduated spacing between the turns; and

Fig. 2 is a modification of the ballast tube of Fig. 1 which comprises a filament having a plurality of equally spaced coils in series and wound to provide successive hotspots for greater ballast control range.

In accordance to the present invention a ballast tube is formed of a glass or metal tube of any desired construction by positioning therein a resistance wire of uniform diameter in cross-section to form a filament made of a metal having a high temperature coefficient of resistance which increases with an increase in temperature such that the resistance of the filament increases more rapidly than the temperature as the voltage across the filament is increased. The filament is supported within the glass or metal tube and has the ends thereof connected to massive leads which extend from the base of the tube. The filament is constructed such that turns wound therein creates a hot-spot which controls the resistance of the filament as the voltage is increased or decreased.

Referring now to the drawings and more particularly to Fig. 1 which illustrates one modification of a ballast tube made according to this invention which comprises a gas filled glass or metal envelope 11 of standard construction filled with any suitable gas such as hydrogen at any suitable pressure. The envelope is secured to an insulating base 12 through which two pins 13 and 14 extend into the inside. The pins connect with two supports 15 and 16 to which the filament 17 is connected. Support 15 is L- shaped and extends upwardly into the tube such that the .L is at the top of the tube and the end thereof is positioned directly above the support 16 to enable connecting filament 17 therebetween. The filament is of a metal having a high temperature coefficient of resistance that increases with an increase in temperature as the voltage across the filament increases, such as tungsten or any other suitable metal, and is formed by a resistance wire of uniform diameter in cross-section in the shape of a helix having a smaller diameter across the helix at the midpoint than at the ends which are connected to the supports. The helix is formed such that a portion of the turns at the midpoint form a uniform coil 18 having a constant diameter with closely spaced turns which turns gradually become farther apart as the diameter of the helix increases uniformly toward the ends at the supports.

The design of the helix is such that a hot-spot is formed at the center thereof due to the closeness of the wires and the smaller diameter of the turns of the coil 18. Such a design prevents the wire filament from becoming distorted during expansion of the midpoint against the supported ends due to the temperature difference between the hot-spot at the midpoint and the supported cooler ends of the filament.

In operation, the tube is placed in a series circuit having a variable voltage supply. The voltage is applied to the circuit and the resistance filament of the tube is heated according to the applied voltage across the tube. Then if a different voltage is applied to the circuit, the resistance of the filament of the ballast tube changes accordingly which changes the increase in voltage to 3 resistance thereby maintaining a constant current across the other parts of the circuit.

Resistance elements according to the present invention will account for decreasing voltage as well as an increasing voltage and the time lag in current stabilization is much less than for straight wire filament tubes of the prior art which do not have the closely wound coil between the supports.

The modification illustrated by Fig. 2 comprises a filament 20 which has a plurality of equally spaced coils 21-24 wound in series and secured within a standard glass tube 30 filled with any suitable gas such as hydrogen at any suitable pressure, The filament is supported in the glass tube by fine wire hooks 25 which space the coils equally throughout the tube and are connected at the ends to massive leads or supports 26 and 27, the ends of which extend beyond the base of the tube and, if needed, are insulated therefrom in any suitable manner. The filament is formed by a resistance wire of any metal having a uniform diameter with a high temperature coefficient of resistance, such as tungsten, which increases in resistance with an increase in temperature as the applied voltage increases. Each coil of the series is formed with the turns wound close enough to cause local heating and development of a hot-spot. The turns are shown as being stretched out for clarity. The turns of the first coil 21 are very close together and the turns of each successive coil 22, 23 and 24 are respectively farther apart, such a relationship causes the coil 21 to create a hot-spot first, then with an increase in voltage, a hot-spot will develop in the next coil 22 and by increasing the voltage over the range of ballast control, hot-spots will develop successively in all of the coils. This construction provides ballast control over a greater range than for a filament having a single helix wound coil as illustrated in Fig. 1.

Operation of the tube of Fig. 2 is such that with the tube in a series circuit, as the voltage is increased the resistance of the filament increases with an increase in temperature which converts the voltage into resistance. As the voltage increases the closeness of the winding of the first coil 21 causes a hot-spot and an increase in resistance of the filament, then as the voltage is increased more, the second coil 22 will develop a hot-spot causing a higher increase in filament resistance. Further increase in voltage will produce hot-spots in the other coils to further increase the resistance of the filament thereby providing a wide range of ballast control.

The construction of the above described modifications will control the current for a decreasing voltage as well as for an increasing voltage. Due to the construction of the filament, a hot-spot is formed by gradual heating to cause an increase in resistance; likewise, gradual cooling causes a decrease in resistance thereby providing a good efiicient ballast tube which regulates current with very little lag in time for stabilizing the current. Tubes made according to this invention can be made with a wire filament having a uniform diameter of one mil and with a hydrogen gas pressure of five millimeters of mercury.

Obviously many modifications and variations of the present invention are possible in the light of the above teaching. It is therefore to be understood, that Within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A current regulating tube comprising a gas filled envelope, a pair of support leads extending from said envelope, a resistance wire of uniform diameter forming a continuous filament made of a material having a high temperature coefiicient of resistance that increases with temperature supported within said envelope and connected at the ends to said support leads, a portion of said wire filament having turns which form a coil, said coil having a uniform diameter with said turns spaced relatively close together, said filament having poltions thereof on opposite sides of said coil which differ from the diameter and the spacing of said turns forming said coil.

2. A current regulating tube comprising an envelope containing hydrogen gas, a pair of support leads extending from said envelope, one of said leads extending longitudinally into said envelope and having an L-shaped upper end, a resistance wire filament made of material having a high temperature coeflicient of resistance that increases with temperature supported within said envelope longitudinally between the end of the L-shaped support and the other support extending from said envelope, said filament being in the form of a continuous helix with a portion at the midpoint thereof formed as a coil, said coil having turns of uniform diameter and spaced relatively close together, said helix increasing uniformly in diameter and spacing from said coil in opposite directions to the ends thereof whereby said filament develops a hot-spot in said coil.

3. A current regulating tube as claimed in claim 2 wherein the wire forming said filament is of uniform diameter in cross-section.

4. A current regulating tube comprising an envelope containing hydrogen gas, a pair of support leads extending from said envelope, a resistance wire filament made of a material having a high temperature coefficient of resistance that increases with temperature supported within said envelope and connected at the ends to said support leads, said filament being formed by a continuous Wire with a plurality of equally spaced wound coils in series and supporting means positioned between each of said coils for positioning said wire filament uniformly within said envelope.

5. A current regulating tube as claimed in claim 4 wherein the turns of each successive equally spaced coil of said wire filament are spaced farther apart and adapted to provide delayed occurrence of hot-spots.

6. A current regulating tube as claimed in claim 5 wherein the wire forming said filament is with a uniform diameter in cross-section.

References Cited in the file of this patent UNITED STATES PATENTS 652,638 Potter June 2 6, 1900 1,470,788 Weeks Oct. 16, 1923 1,617,634 Heany Feb. 15, 1927 1,804,344 Jones May 5, 1931 2,001,498 Meyer et al .a May 14, 1935 2,081,894 Meyer et al May 25, 1937 2,371,696 Levitt Mar. 20, 1945 2,688,681 Nyyssonen Sept. 7, 1954 FOREIGN PATENTS 222,564 Great Britain Oct. 2, 1924 

